The present invention relates to a process for preparing a metal-containing supported catalyst or a supported catalyst component by impregnation of a support material.
The present invention also relates to a metal-containing supported catalyst or a metal-containing supported catalyst component obtainable by this process, a process for preparing polymers based on monomers having a C-C double bond and/or C-C triple bond, and also to the use of the metal-containing catalyst for forming carbon-carbon or carbon-heteroatom covalent bonds.
Supported catalysts are known and are widely used in many areas of industry. For example, they are used in processes for preparing low molecular weight organic chemicals and intermediates.
A further important application area for metal-containing supported catalysts is the preparation of polymers, in particular polyolefins and styrene polymers. Such polymerizations are preferably carried out in the gas phase or in suspension. The catalysts used are, for example, Ziegler catalysts or metallocene catalysts. For the purposes of the present invention, metallocene catalysts are catalysts comprising a metal complex, preferably a transition metal complex, bearing at least one ligand which in turn contains a cyclopentadienyl type structural unit. Examples of such bridged and unbridged ligands are substituted and unsubstituted cyclopentadienyl ligands, substituted and unsubstituted indenyl ligands or substituted or unsubstituted fluorenyl ligands. Metal complexes containing such ligands are known and are described, for example, in J. Macromol Scixe2x80x94Rev. Macromol Chem. Phys., C34, pages 439-514 (1994).
Processes for preparing metal-containing supported catalysts are known. Efforts are made here to ensure that
a) all suport particles are laden with the transition metal,
b) there are no differences in concentration of the metal component within the loaded support particles and
c) all particles have the same concentration of metal component (mg of metal/quantity of particle).
According to the present state of knowledge, such an ideal catalyst should be well suited, for example, to polymerizing olefins since it displays, inter alia, no sintering together of the polymer particles in the reactor (lump formation) and no overheating of the catalyst particles resulting in deactivation of the catalyst.
According to a known method, supported metallocene catalysts can, for example, be obtained by combining a metallocene-containing solution with the support material, stirring the suspension and removing the solvent under reduced pressure (WO-A 94/28034). Here, the solution volume of the impregnation solution is much greater than the pore volume of the untreated support material, so that a readily stirrable suspension is obtained. Although the metallocene component can be completely applied to the support in this method, the catalyst leads, particularly at high loadings, to difficulties in the polymerization process, for example lump formation.
In a further process for applying metallocene catalysts to supports, the metallocene impregnation solution is combined with the support material with the volume of the impregnation solution being no more than the pore volume of the support material. This gives a paste-like mass from which the solvent is removed (WO-A 94/14856). A disadvantage of this process is that the loading of the support material with sparingly soluble metallocenes is unsatisfactory because of the small amount of solvent, the productivity of the catalyst is low and the economics of the polymerization process are still unsatisfactory.
In a third method of applying the catalyst to a support, the metallocene dissolved in a good solvent is precipitated by means of a poor solvent in the presence of the support material and thus precipitated on the surface of the support material and in its pores (EP-A 0 295 312, WO 98/01481). A disadvantage of this process is that large amounts of precipitation liquids (non-solvents) are required in order to deposit the metallocene component on and in the support material. For the preparation of catalysts, the advice given for industrial purposes is to restrict the amount of non-solvent, thereby leaving valuable metallocene component in solution and therefore losing it from the supported catalyst. This method is unsatisfactory in respect of the space-time yield of catalyst and the economics.